While many inventors have worked in this art and have contributed numerous constructions, so far as I know, there is not today in existence a truly efficient, light weight solar collector for heating fluids, that may be manufactured effectively and inexpensively, and which takes up a small amount of area in the horizontal plane by extending upwards or vertically from a compact base. For example, the U.S. Department of Commerce Technical Information Service publication PB-237042, page 49 (1974) states that the total material cost for a flat plate collector for use, for example, in a single family residence is about $3000 while installation costs for such a collector system is over $2000.
The Dow Corning Corporation publication of 1977 entitled, "Dow Corning Silicones Bring Solar Energy Down to Earth," discusses solar systems employing flat plate glass covered collectors used to solar heat heat-transfer liquids. A commercial concern, Mor-Flo Industries, Inc. of 18450 S. Miles Road, Cleveland, Ohio 44128 has published a brochure entitled, "Now. Hot Water for Everybody Under the Sun," in which a typical flat plate collector is illustrated.
Solar collector designs generally comprise a black surfaced radiation absorber covered with one or more pieces of flat plate glass or plastic. The covers may be coated with antireflection layers.
Flat plate glass covers are used in conjunction with several different materials for seals, connections, insulation and the like. The use of varied materials cause operational problems concerned with the different values of coefficient of expansion. The necessary add ons raise the cost considerably.
The known absorbers which are relatively flat and sometimes have fins usually contain within their passages glycol or other common heat exchange fluids. Often the passages for these fluids cause the flat plate absorber to have protuberances in places.
The amount of solar energy collected by these relatively flat absorber plates varies with the season and the hour of the day. Although the solar heat collectors may be designed to move and tilt from the horizontal to obtain maximum impingence of solar rays throughout the day, such a system is very costly and therefore flat absorbers are often fixed in place, lowering their efficiences. The homeowner using them generally sets them at a fixed tilt angle.
When the absorber plate gets hot, it emits radiation which is a heat loss to the system. Air between the flat glass or plastic cover plate and the absorber conducts heat from the absorber to the cover and then to the outside air. This is another heat loss of the system.
Solar reflectors exposed to the weather and environment are damaged by wind carried particles, chemical species in the air and impure rain drops which all alter the reflector's surface and substantially reduce its reflection efficiency and capability.
On Page 43 of Antonin Vasko's book entitled "Infrared Radiation," published by the Chemical Rubber Company Press, Cleveland, Ohio, 1968, is stated that the characteristic of blacks is high absorptance, which with superior blacks can be as great as 99%. Efficiently absorbing blacks for solar absorber purposes are available commercially. Aluminum surfaces may be made black be anodizing. Many metal sulfides are black.